MILWAUKEE (AP) _ A 21/2 -year-old boy who froze almost to death after wandering outside his house in 20 below weather wearing only pajamas is back to his playful self, kicking toys and balloons around his room as he makes medical history, doctors say.

''Our son was dead and he is alive,'' says Judy Troche, the mother of Michael Troche.

On Monday, Milwaukee Children's Hospital upgraded Michael's condition from critical to fair.

Michael was found the morning of Jan. 19 after he wandered from his parents' home in the subzero cold. His body temperature was 60 degrees, compared with the normal reading of 98.6, said Dr. Kevin Kelly, associate director of the pediatric intensive care unit at the hospital.

''When he came in, the legs and arms ... felt like blocks of ice, and as you squeezed the tissue, you could feel ice in the blood, as you would crush ice under the skin,'' Kelly said. He said the blood plasma appeared to have frozen.

At a news conference with the boy's parents Monday, Kelly said there was no known case of an accidental victim of hypothermia surviving a body core temperature that cold.

''Accidental hypothermia has been reported down to 19 degrees Centigrade (66 Fahrenheit), as best we can tell in the world's literature,'' he said. ''No one has any reports less than that.''

Michael faces another three to four weeks in the hospital because of frostbite and skin grafts to his arms and legs, the doctor said.

He said Michael's neurological functions were 100 percent normal. The boy is expected to regain most use of his extremities, although there was an indication of muscle damage to his left hand.

Mrs. Troche had left for her job as a registered nurse before Michael wandered from the home. Her husband, James, was sleeping and their 6-year-old daughter, Chris, was watching television.

Michael may have been outside anywhere from 30 minutes to 31/2 hours, Kelly said. His heart stopped.

''When he was brought into the hospital, he had no vital signs,'' said hospital spokesman Leigh Morris. ''If you didn't know better, you would have said he was clinically dead.''

Oxygenated blood was forced through Michael's body, he was connected to a heart-lung machine to warm his blood, and drugs were used to prevent swelling of brain tissues.

His arms and legs became swollen with fluid from ice-damaged cells, and cuts were made to allow tissues to expand. Skin grafts were used later to heal the cuts and frostbitten areas.

''Probably one of the happiest moments of my life was when they came and told us his heart was beating again'' after about one hour of resuscitation, Mrs. Troche recalled.

It took five hours to warm Michael's body to normal, Kelly said.

Michael gave his first sign of awareness four days later when he nodded his head at the mention of his favorite television show, ''Sesame Street,'' Mrs. Troche said.Within a day, he was able to speak, saying the names of two favorite things, ''gum and popcorn,'' she said.

''He wants to go home,'' said his father.

Michael has regained his playfulness, his parents said.

While he doesn't like the bandages on his hands, ''he is enjoying the splints on his legs,'' Troche said, adding that Michael was using them to kick toys and balloons around his hospital room.

Kelly said therapeutic uses of hypothermia, in which the body is intentionally cooled for certain types of heart surgery, had indicated that it should be possible to have an accident victim like Michael fully recover if the right resuscitation methods were used.

''We knew it was possible, but this really just confirms that it is possible,'' he said.''What's been learned from Michael is going to add a lot to the wealth of knowledge about hypothermia.''